The present invention relates generally to an apparatus and method for retrieving a single small particle from a plurality of particles.
Through combinatorial chemistry scientists can create combinatorial libraries of compounds, en masse, and rapidly test such libraries for physiological or other activity. The combinatorial libraries are generated by successively partitioning a group of solid supports, which are typically embodied as beads having a diameter in the range of about 50 to 1000 microns. With each successive partitioning, the solid supports are uniquely treated, such as by adding a chemical moiety thereto. The partitionings are repeated until a desired combinatorial library is produced. The combinatorial library comprises a large number of library compounds, each of which compounds is attached to a solid support.
For screening purposes, a combinatorial library is typically segregated into a plurality of small groups containing about 1-30 solid supports (i.e., library compounds) per group. The small groups of solid supports are usually retained in collection plates, referred to as microtiter or microwell plates, that have a multiplicity of small wells (e.g., 96-, 384-, 1536-well plates). To segregate a combinatorial library into such small groups, a device for handling a few or even an individual solid support is required. Such a device must be able to reliably withdraw a solid support from a large number of such solid supports contained in a fluid, and then deliver and deposit the withdrawn support to a desired site.
Aside from the difficulties inherent in handling an individual small particle, in the realm of combinatorial chemistry, a further complication arises. In particular, treatments steps (e.g., reaction steps, washing steps, etc.) often increase the tendency of the solid supports to adhere to one another or the transport/delivery means. Such increased adhesion complicates and frustrates individual particle retrieval.
Various devices are available for sorting, counting and retrieving particles from large groups of such particles. Such devices have been used for sorting or counting biological cells (U.S. Pat. Nos. 3,710,933; 4,173, 415; 4,606,631), transferring yeast containing beads (U.S. Pat. No. 4,655,265), dispensing reagent spheres (U.S. Pat. No. 5,616,299), arraying small objects into containers (U.S. Pat. No. 5,649,576), transferring articles contained in a fluid medium (U.S. Pat. No. 5,722,470) and placing a biological reagent on a substrate (U.S. Pat. No. 5,731,152). None of the above-referenced devices reliably retrieves a single particle from a group of such particles, transfers the retrieved particle to a desired destination, and deposits the particle at the desired destination.
More recently, a robot equipped with capillary tubes that pick up beads (i. e., solid supports) using a suction force has been disclosed. While such a device may reliably engage a particle, it will not reliably disengage the particle. More particularly, once a bead is engaged to a capillary tube, various physical phenomena cause an attraction between the bead and the capillary tube that tend to keep the bead engage d to the tube. Simply discontinuing suction will not reliably disengage the bead.
As such, an article and method for reliably retrieving, transferring and depositing a single particle is needed.
Satisfying the aforementioned need, a particle-retrieval device in accordance with the present teachings comprises, in some embodiments, a receiver tube, vacuum-flow providing means and particle-disengaging means. The receiver tube contains a bore or lumen running its full length. The bore is in fluid communication with the vacuum-flow providing means. When flow is introduced into the vacuum-flow providing means, a suction or vacuum flow is developed at the second end of the receiver. For the purposes of this Specification, when a first and a second region are described to be in xe2x80x9cfluid communication,xe2x80x9d it means that fluid flow and/or pressure conditions prevailing in the first region affect fluid flow and/or pressure conditions in the second region.
The suction developed at the second end of the receiver causes a particle to adhere thereto. A particle-engagement site at the second end of the receiver is advantageously physically adapted to receive a single particle.
Once a particle is engaged to the receiver, various physical phenomena work in concert with the continuing suction force to keep the particle engaged. Such physical phenomena cause an increased adhesion between a particle and the receiver. As such, action in addition to discontinuing the suction force is required to reliably disengage a particle from the receiver tube. To that end, a particle-retrieval device in accordance with the present teachings advantageously incorporates particle-disengaging means.
In the illustrated embodiments, the particle-disengaging means advantageously delivers a droplet of liquid that is conducted to and wets an engaged particle. Discontinuing suction and wetting the particle reliably disengages the particle from the receiver.
To retrieve a particle from a source vessel requires that positioning means place the device and vessel in alignment and in sufficiently close proximity such that the suction developed at the particle-engagement site can xe2x80x9cgrabxe2x80x9d a particle. In various embodiments, positioning means are configured to move either the particle-retrieval device, a source vessel or both. In one embodiment, the positioning means is an x-y-z stage.
In addition to the one particle that is engaged at the particle-engagement site, other particles and particle fragments may disadvantageously adhere to the receiver and/or the particle near the particle-engagement site. As such, in some embodiments, the present invention includes an excess particle/fragment remover for removing excess particles and particle fragments. The excess particle/fragment remover can be embodied in a variety of ways that are described later in this specification.
Since the present invention is capable of retrieving very small particles that may be difficult to directly observe, the present invention advantageously includes a particle detector. In one embodiment, the particle detector is realized as a bellows that is in fluid communication with the bore running through the receiver tube. As a particle engages the particle-engagement site at the second end of the receiver tube, pressure within the bore changes. Such a pressure change is observed as a collapse of the bellows (i.e., the bellows xe2x80x9ccompressesxe2x80x9d or decreases in length). The change in bellows length can be detected and indicates that a particle is engaged.
Further features of the present invention will become apparent from the Detailed Description of specific embodiments thereof when read in conjunction with the accompanying drawings, which are described briefly below.